1. Field of the Invention
The present invention relates to a process for adjusting the detecting axis of an object detector that detects an object in a predetermined detecting area provided in a traveling direction of a vehicle by transmitting an electromagnetic wave to the detecting area and receiving a wave reflected from the object.
2. Description of the Related Art
When a radar system used in an adaptive cruise control system (ACC system), a traffic snarl follow-up system (Stop and Go system), an inter-vehicle distance warning system and other such systems are mounted to a vehicle, if an object detecting axis of the radar system is not correctly oriented to a preset direction, several problems may occur. For example, an on-coming vehicle in an adjacent lane may be erroneously detected, wherein the system is incorrectly operated. Additionally, the system may only detect a road surface, a bridge or a signboard. Moreover, the system may not detect a vehicle traveling ahead of a subject vehicle (a preceding vehicle), wherein the system is not operating.
A system that conducts an aiming operation for aligning an object detecting axis of a radar system with a preset direction is disclosed in Japanese Patent Application Laid-open Nos. 9-178856 and 11-38140. The disclosed system is designed to aim the object detecting axis of the radar system by stopping a vehicle to assume a predetermined positional relationship to a reference reflector; receive a reflected wave resulting from an electromagnetic wave transmitted from the radar system reflecting off of a reference reflector; detect the direction of the object detecting axis of the radar system from the detected direction of the reference reflector; and then align the direction with a preset direction.
In the conventional aiming process, a reference reflector R is positioned on the centerline L of a vehicle and 5 m forward of a front end of a vehicle V, as shown in FIG. 13A. However, the conventional aiming process requires no object, other than the reference reflector R, to be located in an aiming space that spans an area approximately 15 m from the front end of the vehicle and laterally 2 m from the centerline L of the vehicle. Therefore, a large space having a length of about 20 m and a width of 4 m, including the area covered by the vehicle V, is required, as shown in FIG. 13B.
If an object other than the reference reflector R exists in a detecting area for the radar system Sr, the radar system Sr detects both the reference reflector R and the object, as shown in FIG. 14A. As a result, the radar system Sr and the object cannot differentiate between the reference reflector R and the object, as shown in FIG. 14B. Therefore, there is a possibility that the object may be misidentified as the reference reflector R upon which to base the aiming process, resulting in the object detecting axis Ar of the radar system Sr being erroneously positioned.
If another object exists close to the reference reflector R and within the detecting area for the radar system Sr, as shown in FIG. 15A, the radar system Sr detects the reference reflector R and the object as a single object, as shown in FIG. 15B. Therefore, there is a possibility that the central position of the detected object may be misrecognized as the position of the reference reflector R upon which to base the aiming process, resulting in the object detecting axis Ar of the radar system Sr being erroneously positioned.
When a wall reflecting an electromagnetic wave is ahead of and relatively near the reference reflector R because an aiming space having a sufficient length cannot be located, as shown in FIG. 16, a wave reflected from the reference reflector R and a wave reflected from the wall merge, resulting in the position of the reference reflector-R not being recognized such that the aiming process cannot be performed.
Accordingly, it is an object of the present invention to overcome the above-described drawbacks of the related art.
Additionally, it is an object of the present invention to ensure that even when an aiming space having a sufficient length cannot be located, an accurate aiming process can be executed.
To achieve the above objects, according to a first aspect and feature of the present invention, there is provided a process for adjusting a detecting axis of an object detecting means for detecting an object present in a predetermined detecting area established in a traveling direction of a vehicle. An electromagnetic wave is transmitted to the detecting area and then receives a wave that is reflected from the object. The process includes a disposing step wherein a reference reflector is disposed at a predetermined location in front of an object detecting means that is mounted on a vehicle and disposing an electromagnetic wave absorber ahead of and in proximity of the reference reflector. The electromagnetic wave absorber has an extent that includes the entire projected image of the reference reflector. Additionally, there is an adjusting step wherein an object detecting axis of the object detecting means is adjusted so that the reference reflector assumes a reference position for the detecting area.
With this arrangement, in a state in which the electromagnetic wave absorber is disposed ahead of and in proximity of the reference reflector, which itself is disposed in front of the object detecting means mounted on the vehicle, the electromagnetic wave is transmitted from the object detecting means to adjust the object detecting axis of the object detecting means so that the reference reflector assumes the reference position for the detecting area. Therefore, it is not required that an aiming space, where no object reflecting the electromagnetic wave exists, be widely secured ahead of the reference reflector. Further, even when an aiming space having a sufficient length cannot be secured, an accurate aiming process can be executed.
According to a second feature of the present invention, a face of the electromagnetic wave absorber positioned on the side of the object detecting means is columnar. With this arrangement, the reflection of the electromagnetic wave from the electromagnetic wave absorber is minimized while the electromagnetic wave absorber reliably obtains the projected image of the reference reflector.
According to third and fourth features of the present invention, the electromagnetic wave absorber has a height ranging over a vertical width of the detecting area in a position where the electromagnetic wave absorber is disposed. With this arrangement, the electromagnetic wave absorber has the height ranging over the vertical width of the detecting area for the object detecting means. As a result, the electromagnetic wave is reliably prevented from being reflected off an object other than the reference reflector.
According to fifth to eighth features of the present invention, the electromagnetic wave absorber is black. With this arrangement, the electromagnetic wave absorber more effectively absorbs near infrared rays, which are waves transmitted by a laser radar system.
According to ninth and tenth features of the present invention, the electromagnetic wave absorber comprises a tire. With this arrangement, the electromagnetic wave absorber has a black color and effectively absorbs near infrared rays. Furthermore, the electromagnetic wave absorber also has an enhanced absorbability for a millimeter wave of a millimeter radar device since carbon black is contained in the tire. Additionally, the electromagnetic wave absorber can be constructed to have any height by stacking a plurality of the tires on top of each other. Moreover, the electromagnetic wave-reflecting face is the columnar face, thus, the reflection of the electromagnetic wave is minimized.
A radar system Sr in each of embodiments corresponds to the object detecting means of the present invention, and tires T in each of the embodiments correspond to the electromagnetic wave absorber of the present invention.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.